In the LTE and the LTE-A standards, the system frame of the TDD is made up of ten sub-frames. The 3GPP supports a total of 7 kinds of frame structure together, as shown in Table 1.
TABLE 1uplink and downlink frame structures of the TDD systemSwitchingSerialpointnumbersperiod fromfordownlinkSub-frame numberuplinkto uplink012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
In the current 3GPP standard, system information SIB-I is used to inform the UE of the frame structure configured for the current serving cell. According to the existing standard, the minimum change period of the SIB information is 640 ms. In pre-research project of the “Dynamic TDD frame structure” formally approved by the 3GPP in the RAN54 (December of 2011) plenary session, it becomes possible to allocate the frame structures of the TDD system more dynamically. Shortening the change period of the frame structure of the TDD system can take full advantage of the characteristics of the TDD to support the transmission of the anti-symmetrical service.
But there is no specific scheme on how to set the retransmission of the downlink data frame. In addition, in the process of the uplink synchronization HARQ, how to retransmit the PUSCH to avoid the conflict with the R10 UE needs a further solution as well.